The present invention relates, in general, to the treatment of flue gas, and in particular to a new and useful system and method for protecting gas-gas heaters used in conjunction with flue gas desulfurization systems.
It is a well-established practice to use gas-gas heaters for transferring heat from untreated flue gas to treated flue gas in wet flue gas desulfurization systems. The materials used in the gas-gas heaters comprise materials such as corrosion-resistant alloys or lined, low-alloy, carbon steel. Normally, a gas-gas heater is exposed to flue gas leaving the boiler train at a normal temperature range of 200.degree.-350.degree. F.
However, in case of an upset, such as an air heater drive failure, the temperature of the flue gas can increase to above the normal temperature range and in some cases exceed 700.degree. F. When this occurs, the lining used in the gas-gas heater is unable to tolerate these higher temperatures and is severely damaged and sacrificed.
In an effort to prevent damage to the gas-gas heaters, higher alloys such as 317L stainless or Hastelloy.RTM. C-22 have been used to accommodate the higher temperatures. As expected, these higher alloys are expensive and provide a costly process when manufacturing and/or retrofitting gas-gas heaters using these alloys.